Magnetic proximity switch



United States Patent Office 3,398,384 MAGNETIC PROXIMITY SWITCH LeonardPiekarski, Pomona, Calif., assignor of one-fourth each to Irving B.Collins, Los Angeles, Veronica Whitesides, Culver City, T. A. Smith,Long Beach, and Carroll E. Isham, Buena Park, Calif.

Filed Mar. 4, 1966, Ser. No. 531,878 3 Claims. (Cl. 335-207) Thisinvention relates to an improved proximity device, for automaticallyactuating an electrical circuit in a predetermined manner in response tothe movement of a body of magnetic material into the vicinity of thedevice. It is contemplated broadly that the device may be applied to anyof numerous different uses, in Which response to the presence of a bodyor bodies of magnetic material is desirable, for instance in countingitems passing along a conveyor system, in sorting items, or the like;but the inventon will be described primarily and typically as utilizedin responding to the movements of a motor Vehicle, as for parkingcontrol or trafiic control purposes.

Though numerous types of magnetically actuated proximity devices orswitches have been proposed in the past, great difficulty has beenencountered in attempting to render such devices sufficiently reliablein operation to be certain under all conditions that the device willrespond properly to a particular change in conditions. For example, manyof these prior devices have been so insensitive as to require movementof an automobile or other body of magnetic material into such closeproximity to the device as to render it useless for most practicalpurposes. Other previously proposed devices have been so non-positive orindecisive in operation that their actuation from one condition toanother could not be relied upon as a definite indication of thepresence or absence of magnetic material in the vicinity, since thesedevices may sometimes respond properly and other times fail to respond.

A major object of the present invention is to provide an improvedproximity device which is considerably more reliable in its operationthan any of the various prior arrangements with which I am acquainted. Aunit embodying the invention functions in such a positive manner as toinvariably produce the proper response to the presence of magneticmaterial within the vicinity, and to reliably and invariably produce areverse response to the absence of such material. Additionally, thedevice functions on a principle giving it very great sensitivity, sothat it may be utilized for response to the presence of magneticmaterial within a very substantial distance of the device, and notnecessarily require movement of the magnetic material into extremelyclose proximity to the device.

structurally, a unit embodying the invention includes at least onemagnet (preferably a number of such magnets) mounted to swing between anormal position of essential alignment with an ambient magnetic field,such as the earths field, and a deflected position, in response tomovement of a body of magnetic material into the vicinity of the magnetor magnets. In conjunction with these magnets, I utilize electricalswitching means which are operable magnetically by the field of theswinging magnet or magnets in a manner opening or closing an electricalcircuit upon deflection of the magnets from their normal position. Theswitching means preferably include a reed switch, which responds in apositive and reliable manner to slight swinging movement of the magnetsfrom their normal position. The sensitivity of the reed switch may beincreased by positioning near that switch a biasing magnet, whichextends transversely of the contacts of the reed in a manner enablingthe device to respond to very slight swinging movement of the mainmagnet or magnets.

3,398,384 Patented Aug. 20, 1968 Another feature of the inventionrelates to a preferred bearing structure for mounting the swingingmagnets, or more broadly for mounting any of numerous different types ofpivotal elements, in a manner minimizing the friction of the movingpart, and preventing binding of that part. For this purpose, I employtwo interfitting hearing parts, one of which forms a socket recess intowhich a projection on the other part extends in bearing relation. Theprojection has an essentially transverse end surface engageable againstan inner end surface of the socket recess, but with the parts beingspaced radially apart as their surfaces advance axially from thementioned end surface areas. This leaves minute clearance spaces aboutthe periphery of the projection in a manner preventing the developmentof excessive friction between the parts by the presence of smallparticles of dust or the like in the bearing areas.

To avoid disturbance of the magnetic characteristics of the discussedproximity device, I prefer to form the pivotal mounting hearing orbearings of a nonmagnetic material, such as sapphire, so that magneticflux cannot flow through these hearings.

The above and other features and objects of the invention will be betterunderstood from the following detailed description of the typicalembodiment illustrated in the accompanying drawing, in which:

FIG. 1 shows somewhat diagrammatically the manner in which a deviceembodying the invention may be utilized for response to the presence ofan automobile or other motor vehicle;

FIG. 2 is an enlarged plan view of the detector device of FIG. 1,partially broken away to reveal its inner construction;

FIG. 3 is a vertical section taken on line 33 of FIG. 2;

FIG. 4 is a further enlarged fragmentary vertical section taken on line4-4 of FIG. 2;

FIG. 5 is a greatly enlarged axial vertical section through one of thebearings for mounting the swinging magnets; and

FIG. 6 is a horizontal section taken on line 66 of FIG. 4.

With reference first to FIG. 1, I have illustrated at 10 a proximitydevice or detector constructed in accordance with the invention, andrepresented as buried within a roadbed 11, at a location spaced beneaththe upper horizontal road surface 12 along which automobiles 13 andother motor vehicles travel. vThe device 10 may typically be buried afew inches (say for example about six inches) beneath'road surface 12,and is adapted to respond automatically to the movement of automobile 13to a position over device 10, by virtue of the alteration of the ambientmagnetic field resulting from the presence of the steel or othermagnetic material constituting the body and other parts of theautomobile.

As seen best in FIGS. 2 and 3, the proximity device 10 may have an outerhousing 14, preferably formed of an appropriate rigid nonmagneticmaterial such as a fiberglass reinforced resinous plastic material.Housing 14 is typically represented as of cylindrical configuration,having a vertically extending cylindrical side wall 15 centered about avertical axis 16, and having top and bottom horizontal walls 17 and 18,with these three walls 15, 17 and 18 desirably being fluid imperviousand sealed at their contacting edges and other points in a fluid tightrelation effectively hermetically sealing the interior of the housingfrom its exterior.

Extending diametrically across the interior of housing 14, there isprovided a rigid frame structure 19 (FIGS. 2 and 3), which movablymounts a swinging magnet assembly 20 for pivotal movement about verticalaxis 16.

rrame structure 19 may include two upper and lower typically identicalrigid horizontal elements 21 and 22, extending diametrically across thecylindrical housing in vertically spaced and parallel relation. Theseparts 21 and 22 are maintained in their illustrated vertically spacedrelation by two tubular spacers 23 at their opposite ends, with twoscrews 24 extending vertically through and being sealed with respect toapertures 25 in bottom wall 18 of the housing, and then through bottomframe part 22, spacer tubes 23, and top frame part 21, and with theupper ends of these screws being connected to nuts 26 in a mannersecurely holding all of the parts 21, 22 and 23 in their illustratedrelative positions, and in fixed positions relative to the housing. Theparts 21, 22 and 23, as well as screws 24 and nuts 26, may all be formedof an appropriate rigid but nonmagnetic material, such as brass.

Magnetic assembly 20 includes several desirably identical magnets 27,which may be cylindrical as shown, and elongated along a series ofindividual horizontally extending parallel north-south axes 28 of themagnets. These magnets have north poles at a first en-d, say for examplethe left ends of all of the magnets as illustrated in FIG. 2, and havesouth poles at their opposite ends, so that they all tend to normallyswing to a predetermined position of alignment with the horizontalcomponent of the earths field or other ambient field in the vicinity ofthe device. This normal ambient-field-aligned position of the magnets isthe position illustrated in full lines in FIG. 2.

The magnets 27 are all carried by a common carrier element 29, which maybe a horizontally elongated piece of rigid desirably nonmagnetic metal.This carrier element 29 may contain a series of identical horizontallyspaced aligned circular openings 30 through which the various magnetsextend, and within which the magnets are rigidly held by appropriatewelding, brazing, or other suitable ineans. Carrier element 29 is inturn rigidly secured to and mounted by a vertical mounting shaft 31,Which may extend through and be welded or otherwise secured within avertical passage 32 in carrier element 29, and which extends along andis rotatable about vertical axis 16 of the device. The upper and lowerends of the shaft 31 are pivotally mounted by a pair of upper and lowerbearings 33 and 34, which may be identical and are screwed into verticalthreaded passages 35 and 36 in frame elements 21 and 22 respectively.

As seen best in FIG. 5, the upper bearing 33 includes a first part 37having external threads 38 which are screwed into threaded passage 35 inpart 21, with part 33 being adjustable within part 21 by means of ascrewdriver received within a screwdriver slot 39. At its underside,part 33 of the hearing has a typically cylindrical recess 40 centeredabout vertical axis 16, and containing a bearing element properdesignated 41. Element 41 is a pressed fit within recess 40, or isotherwise secured in fixed position within that recess, and is desirablyformed of a nonmagnetic and noncorrosive material, preferably sapphire.Externally, bearing element 41 is shaped cylindrically in conformancewith the recess. Internally, this bearing element contains a socketrecess 42 within which a tapered upper end portion 43 of shaft 31 ispivotally received. Recess 42 is centered about axis 16, and is ofcircular cross section, and has at its upper end an upper or inner Wallsurface 44 desirably disposed directly transversely of axis 16 anddefined peripherally by a circular edge 45 of that surface. Radiallyoutwardly beyond circular edge 45 of transverse surface 44, socketrecess 42 has an annular side wall surface 46, which may advanceprimarily radially outwardly at a location 47 directly adjacent to edge45, but which then curves progressively in a more axially extendingdirection as seen in FIG. 5, to ultimately extend primarily axially at48.

The tapering portion 43 of shaft 31 which extends into socket recess 42may have an upper bearing surface 49 desirably disposed directlytransversely of axis 16, and engaging upwardly against surface 44 ofbearing element 41. As in the case of surface 44, the surface 49 ofshaft 31 is desirably circular, terminating in a peripheral circularedge 50, but of a diameter somewhat less than the diameter of surface44. Beyond this edge 50 of surface 49, shaft 31 has an annular taperingsurface 51, which gradually curves to extend in a progressively lessradial and more axial direction as this surface advances downwardly inFIG. 5. It is also noted that surface 51 preferably extends moredirectly axially at the location 52 directly adjacent edge 50 than doessocket wall surface 46 at its corresponding radially opposite location47.

The diameters of inner surface 46 of the socket recess and outer surface51 of the shaft 31 differ sufiiciently to provide radially between thesesurfaces an annular clearance space 53, which extends entirely aboutshaft 31 and which desirably extends the entire axial length of bearingelement 41 from the plane of transverse surface 44 to the lowerextremity of that element 41. Though this clearance space appears in thefigure to be of very substantial width, it is actually very narrow. Forexample, it is preferred that the difference in diameter between the twoend surfaces 44 and 45 be no more than a few thousandths of an inch, sayfor example no more than three thousandths. Thus, in a preferred form ofthe invention, surface 49 has a diameter of five thousandths, whilesurface 44 has a diameter of seven thousandths, and the clearance space53 between the two bearing parts may have an average radial extent ofapproximately two thousandths of an inch.

The lower bearing 34 may be identical with the upper bearing 33, whichhas been described above in detail and is illustrated in FIG. 5.Similarly, the lower end of shaft 31 may be tapered in the same manneras. its upper end, to have the same interfitting relationship with thelower bearing as is illustrated in FIG. 5.

To the upper side of top frame part 21, there is mounted a reed switch54, which may be contained and encapsulated within a block 55 of anappropriate nonmagnetic rigid resinous plastic material. This block 55may have ears or tabs 56 by which it is secured rigidly to frame part21, by means of screws represented at 57.

As seen clearly in FIG. 4, the reed switch 54 may be of a completelyconventional well known construction, including an outer horizontallyelongated glass tube closed at its opposite ends in fluid tight sealedrelation, and containing two flexible metal reed contacts 57' and 58extending essentially along a horizontal axis 59 from opposite ends oftube 56. The inner free ends 60 of the two reed contacts 57' and 58 arenormally received in the slightly spaced relation illustrated in FIG. 4,so that the switch is open at this point. In response to the developmentof a magnetic field in the vicinity, having a suificient component inthe direction of axis 59 to actuate the switch, the adjacent ends 60- ofreed contacts 57' and 58 are magnetically actuated toward one anotherand into engagement, to thereby close the circuit through the switch andbetween the two leads 61 and 62 at opposite ends of the reed switch. Asseen in the figures, the reed switch 54 is so mounted that itslongitudinal axis 59 extends transversely of the north-south axes 28 ofmagnets 27, when the magnets are in their FIG. 2 full line normalpositions.

For increasing the sensitivity of reed switch 54 to slight deflectionsof magnets 27, I provide closely adjacent and preferably slightly abovethe reed switch a biasing magnet 63 (FIG. 4), which may be embeddedwithin and located in fixed position by plastic block 55. Magnets 63 maybe elongated along a north-south axis 64 (FIGS. 2 and 6), which isdisposed transversely of and slightly above axis 59 and the reed switch,and which is parallel to north-south axes 28 of the main magnets 27 whenthe latter are in their full line normal position of FIG. 2. Thepolarity of biasing magnet 63 should however be reversed as comparedwith magnets 27 (in their normal position), so that the south pole ofmagnet 63 is to the left in FIG.

2, and its north pole is to the right. Biasing magnet 63 is of coursemuch weaker in magnetic strength than are the combined magnets 27, orfor that matter the individual magnets 27.

The two electrical leads 65 from opposite ends of reed switch 54 areconnected through sealed water tight and fluid tight terminals 66 to theexterior of housing 14, and are then connected by external leads 67(FIG. 1) into a series circuit including a battery or other source ofelectrical energy 68 and an appropriate indicator device 69 adapted toprovide an indication of the magnetic actuation of detector switch 10.Indicator 69 may for example be a light or audi-ble signal indicatingthat the switch has been actuated, or may be an automatic piece ofparking control or trafllc control equipment, or the like, adapted torespond in predetermined manner to actuation of the switch.

To now describe a cycle of operation of the switch, assume first of allthat the automobile 13 of FIG. 1 is not present, within the responsezone of proximity unit 10, and that magnets 27 are therefore initiallyretained in their full line normal positions of FIG. 2, in which theyare aligned with the horizontal component of the ambient earths magneticfield, or other ambient field. In this condition, reed switch 54 isopen, and indicator 69 is therefore not energized. If an automobile 13now advances into proximity to device 10, the magnetism of theautomobile will act to cause magnets 27 and their mounting verticalshaft 31 to swing about vertical axis 16 to a defiected position, suchas the broken line position of FIG. 2. This swinging of the magnets 27causes their individual and composite magnetic fields to turn about axis16, and since reed switch 54 is within the magnetic fields of magnets27, these fields will at some deflected position have the effect ofclosing contact 60 of the reed switch and therefore energizing indicator69. It is found that a very few degrees of deflection of magnets 27 canhave this desired efiect, say for example five to ten degreesdeflection, particularly in the presence of the biasing magnet 63, whichis also close enough to the reed switch that the latter is within themagnetic field of the biasing magnet.

The unique bearing structure illustrated in FIG. 5 mounts the magnetassembly for very low friction turning movement about axis 16, and byvirtue of the provision of the clearance space 53 within the bearingassemblies, has the effect of preventing binding of the bearings such asmay result in other arrangements due to the presence of dust particlesor the like in the bearings.

It will be understood that reed switch 54, in addition to being withinthe field of magnets 27, is also of course subjected directly to themagnetic field of the automobile 13. However, this field of the vehicleis, at the switch location, necessarily relatively weak as compared withthe field of magnets 27, and is not great enough to actuate the reedswitch directly, but will cause actuation of the switch indirectly inthe discussed manner, by first swinging magnets 27 and then operatingthe switch by the field of these magnets.

I claim:

1. A proximity device comprising at least one magnet mounted to swingbetween a normal position of essential alignment with an ambient fieldand a deflected position in response to movement of a body of magneticmaterial into the vicinity of the magnet, and magnetically actuatedelectrical switching means positioned near said magnet and operablemagnetically by the field of said magnet to open or close an electricalcircuit upon deflection of said magnet from said normal position, saidmagnet having a North-South axis which in said normal position isessentially aligned with said ambient field, said switching meansincluding a magnetically actuated reed switch located near said magnetand having reed contacts disposed essentially transversely of saidNorth-South axis of the magnet when the magnet is in said normalposition.

2. A proximity device comprising at least One magnet mounted to swingbetween a normal position of essential alignment with an ambient fieldand a deflected position in response to movement of a body of magneticmaterial into the vicinity of the magnet, and magnetically actuatedelectrical switching means positioned near said magnet and operablemagnetically by the field of said magnet to open or close an electricalcircuit upon deflection of said magnet from said normal position, saidswitching means including a reed switch having reed contacts extendingin generally a predetermined direction, and a biasing magnet located inclose proximity to said reed switch and having a North-South axisdisposed essentially transversely of said predetermined direction.

3. A proximity device comprising a plurality of magnets connected.together in essentially parallel relation, bearing means mounting saidmagnets for swinging movement in unison about an essentially verticalaxis between a normal position of essential alignment with an ambientfield and a deflected position in response to movement of a body ofmagnetic material into the vicinity of the magnet, said magnets havingspaced parallel North-South axes which in said normal position areessentially aligned with said ambient field, and magnetically actuatedelectrical switching means positioned near said magnets and operablemagnetically by the field of said magnets to open or close an electricalcircuit upon deflection of said magnets from said normal position, saidswitching means including a reed switch located near said essentiallyvertical axis but vertically oflset from said magnets and havingmagnetically actuated reed contacts extending essentially transverselyof said North-South axes of the magnets when the latter are in saidnormal position, said switching means including a fixed biasing magnetlocated closer to said reed switch than are said swinging magnets andhaving much less magnetic force and having .a North-South axis disposedessentially transversely of said reed contacts and essentially parallelto but reversed in polarity with respect to said North-South axes ofsaid swinging magnets when the latter are in said normal position.

References Cited UNITED STATES PATENTS 2,681,960 6/1954 Ellison 335--583,198,902 8/1965 Deshautreaux 335-207 3,249,713 5/1966 Briggs 3351532,489,113 11/ 1949 Veenstra 335-207 3,254,175 5/1966 Todd 335-205BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner.

1. A PROXIMITY DEVICE COMPRISING AT LEAST ONE MAGNET MOUNTED TO SWINGBETWEEN A NORMAL POSITION OF ESSENTIAL ALIGNMENT WITH AN AMBIENT FIELDAND A DEFLECTED POSITION IN RESPONSE TO MOVEMENT OF A BODY OF MAGNETICMATERIAL INTO THE VICINITY OF THE MAGNET, AND MAGNETICALLY ACTUATEDELECTRICAL SWITCHING MEANS POSITIONED NEAR SAID MAGNET AND OPERABLEMAGNETICALLY BY THE FIELD OF SAID MAGNET TO OPEN OR CLOSE AN ELECTRICALCIRCUIT UPON DEFLECTION OF SAID MAGNET FROM SAID NORMAL POSITION, SAIDMAGNET HAVING A NORTH-SOUTH AXIS WHICH IN SAID NORMAL POSITION ISESSENTIALLY ALIGNED WITH SAID AMBIENT FIELD, SAID SWITCHING MEANSINCLUDING A MAGNETICALLY ACTUATED REED SWITCH LOCATED NEAR SAID MAGNETICAND HAVING REED CONTACTS DISPOSED ESSENTIALLY